Power limiting arrangement in a sewing machine

Abstract

A sewing machine is disclosed in which electromechanical actuators are incorporated. By selectively supplying power to position the electromechanical actuators, the stitch forming instrumentalities of the sewing machine may be operatively controlled. In order to reduce heat dissipation within the sewing machine under abnormal conditions where the actuators are locked for long periods of time, the sewing machine main drive motor motion is monitored. After a predetermined period of inactivity of the sewing machine main drive motor, the power which can be supplied to the actuators is limited.

We claim: 
     
       1. In a sewing machine having a stitch forming instrumentality operatively controllable by supplying power to position an electromechanical actuator: means for sensing operation of the sewing machine and providing an operation signal representative thereof; and   power limiting means responsive to the absence of said operation signal for a predetermined time interval for placing an upper limit on the power supplied to said actuator.   
     
     
       2. The sewing machine according to claim 1 wherein said sensing means includes means for detecting the revolution of the sewing machine main drive motor and providing said operation signal in timed relation thereto. 
     
     
       3. The sewing machine according to claim 1 wherein a plurality of operator selectable patterns may be sewn and said sensing means includes means responsive to operator selection of a pattern for providing said operation signal. 
     
     
       4. The sewing machine according to claim 1 wherein said sensing means includes means responsive to power being applied to said sewing machine for providing said operation signal. 
     
     
       5. The sewing machine according to claims 2, 3 or 4 wherein said power limiting means includes: clock means for providing clock pulses at a fixed frequency;   counter means for counting said clock pulses;   means responsive to said counter means reaching a predetermined count for reducing said power; and   means responsive to said operation signal for resetting said counter means.   
     
     
       6. The sewing machine according to claim 1 wherein said power limiting means includes means for duty cycle modulating the voltage applied to said actuator. 
     
     
       7. The sewing machine according to claim 1 wherein said power limiting means includes voltage divider means selectively connectable in a power supplying path for said actuator. 
     
     
       8. The sewing machine according to claim 7 wherein said voltage divider means includes: a first resistor serially connected in said path;   a second resistor connected between a reference voltage and the end of said first resistor electrically closest to said actuator;   normally open switch means connected in series with said second resistor; and   means responsive to the absence of said operation signal for said predetermined time interval for closing said switch means.   
     
     
       9. The sewing machine according to claim 1 wherein said power limiting means is only operative under a condition wherein power above a predetermined level is supplied to said actuator. 
     
     
       10. The sewing machine according to claim 9 wherein said actuator is a needle bar release solenoid, said predetermined power level is zero power, and said power limiting means includes means for duty cycle modulating the voltage applied to said solenoid.